Regional climate variation and weather

In what ways does the climate vary across Antarctica and why? What weather
phenomena occur in different parts of the continent?

Warm up

There are large variations in climate across the continent owing mainly to
differences in latitude, altitude, and distance from the Southern Ocean. The
Antarctic climate as a whole can be discussed in terms of three different climate
areas: the interior climate, the coastal climate and the climate of the Antarctic
Peninsula.

The coldest and driest areas are inland, where the ice sheets form high plateaux
(exceeding 4000m altitude on the East Antarctic Ice Sheet). In these areas,
extremely cold air descends to create persistent high pressure that brings
settled conditions with relatively low wind speeds. Temperatures during the austral summer rarely exceed -20°C and during the winter months temperatures
are often around -60°C. Precipitation is usually snow in the form of 'diamond
dust' – tiny ice crystals formed from the sublimation of water vapour in a
clear, but intensely cold atmosphere – averaging less than 50mm (water equivalent)
per year.

Near the coast there is greater seasonal variation in temperature, and in
the austral summer, temperatures can warm to around 0°C. Due to the lower altitude
and latitude the air is warmer than inland, so enabling it to hold a lot more
water vapour; and in addition, storm systems from the Southern Ocean have more
influence. Hence, annual precipitation is much higher than inland, reaching
levels of around 400mm in some coastal locations, and skies are often cloudy.
Precipitation is almost always in the form of snow, with rain only falling
extremely rarely in some areas in the summer months. Winds can reach high velocities
in areas near the coast due to topographic factors and the phenomenon of katabatic winds discussed further below.

The Antarctic Peninsula extends into the Southern Ocean and is therefore more
influenced by the sea than other parts of the continent. Annual precipitation
varies greatly across the Peninsula, with some areas receiving as little as
250mm water equivalent, and other areas as much as 5000mm. Near the tip of
the peninsula (which lies outside the Antarctic Circle) summer temperatures
often rise a little above freezing.

The harsh weather of Antarctica makes living and working there a real challenge.
Learn about how Antarctic scientists dress for the weather by clicking
here:

The cold facts

Regional measures of temperature and precipitation

Compared with other continents, places in Antarctica where the weather is measured
regularly are few and far between (although the placement of automatic weather
stations and satellite-based weather measurements are improving coverage
of the continent). Of the weather stations that exist, most have relatively
short records. As noted in Section 2.1, strict conditions need to be met
for weather recordings to be classed as 'official' for statistical purposes,
and climatologists like to base any statements about the climate of an area
(the 'average weather' experienced at a locality) on at least 30 years of
data (the '30 year mean'). There are, however, some stations in Antarctica
that meet these stringent requirements and allow scientists to build up a
picture of how temperature, precipitation, and other climate measures vary
across the continent. A few stations have records extending back well beyond
30 years, and these stations are crucial for studies of climate change as
described in Section 2.3.

Important stations where weather is recorded in the interior of the continent
include the Amundsen-Scott station (USA) at the South Pole and the Vostok station
(Russia) in East Antarctica. Both stations were established in 1957 as part
of the International Geophysical Year. The Amundsen-Scott station is at an
elevation of 2900m above sea level and the Vostok station is at 3500m. In addition
to being very cold, these stations also represent the extreme of the polar
desert climate with very low levels of humidity and precipitation. Weather
conditions characteristic of coastal areas of the continent are represented
at Halley station (UK) bordering the Weddell Sea, which has been in operation
since 1956 and McMurdo station (USA) bordering the Ross Sea, also started in
1956. Also on the coast, the Mawson station (Australia) was set up in 1954
and is the oldest continuously occupied station inside the Antarctic Circle.
This station is also notable for the force of the katabatic winds (explained
below) that come down off of the high ice sheet: gusts of wind here can sometimes
be over 100mph. The Rothera station (UK) provides data on the climate of the
Antarctic Peninsula. It is located on the west side of the peninsula at Rothera
Point on Adelaide Island and has been in operation since 1975. Peninsula weather
recordings have been taken over a longer period of time at Vernadsky station
(Ukraine) which was previously a British station called Faraday (the climate
data are sometimes referred to as being from Faraday/Vernadsky). There are
also other stations along the Peninsula, notably the Palmer station (USA) and
the San Martin station (Argentina). There are stations on several islands off
the coast of Antarctica that provide data on the weather and climate of the
Southern Ocean, for example Signy station (UK) on Signy Island in the South
Orkney Islands, first occupied in 1947. Data from a selection of stations are
contained in the spreadsheet attached to Student Activity 2 below.

Winds

The dominant pattern of atmospheric circulation over Antarctica involves cold
air sinking in the interior and then moving away from this area of high pressure
towards the edges of the continent. The air that sinks down onto the interior
is replaced by air from aloft that has travelled southwards at a higher altitude.
This large-scale circulation of air is often referred to as the polar cell.
(There is also a polar cell in the Arctic.) As air from the interior moves
outwards across Antarctica, it doesn't travel directly from south to north.
Instead, the direction of the air is deflected by the Earth's rotation to
form polar easterlies, meaning that the prevailing wind direction is from
east to west across much of the continent. This occurs because the Coriolis
Force causes air to be deflected to the left of its 'pressure gradient path'
(the most direct route from high to low pressure) in the Southern Hemisphere.

Where these easterly winds approach the coast they can reach high velocities.
A katabatic wind refers to cold and relatively dense air near the surface moving
downhill due to gravity. Across much of the gently sloping ice sheet katabatic
winds average about 10 miles per hour; but towards the edges of the continent,
slope gradients become steep and air can be funnelled down into coastal valleys
causing much higher average velocities. In some places the average annual wind
velocity is nearly 50 miles per hour!

Moving northwards, away from the continental interior, the polar easterlies
eventually give way to the zone of westerly winds affecting the Southern Ocean.
The westerly winds are associated with the low pressure area (circumpolar trough)
that surrounds the continent owing to the large temperature difference between
cold polar air and milder air from the southern mid-latitudes. The circumpolar
trough exists because where warmer air meets the cold polar air (along the
polar front) the warmer air is forced upwards, creating lower pressure at sea
level and the frequent storm systems that affect the Southern Ocean. Air moving
from the mid-latitudes towards the circumpolar trough is deflected to the left
by the Coriolis force thereby producing the westerly prevailing winds. The
westerly winds and Southern Ocean storm systems affect parts of the Antarctic
coastline, the Antarctic Peninsula, and the islands off the coast of Antarctica.

Other weather phenomena

Antarctica is also known for several intriguing types of atmosphere and weather
phenomena.

Aurora Australis

Known as the Aurora borealis in the Northern Hemisphere,
this spectacular phenomenon is often described as waving or shimmering curtains
of light across the night sky. It is caused by charged particles from the Sun
being pulled towards the Earth's magnetic poles and interacting with gases
high in the atmosphere to illuminate the night sky.

Diamond dust

This occurs when water vapour sublimates directly out of
the cold atmosphere to form ice crystals, creating a form of precipitation
that occurs under clear skies.

Halo

This optical phenomenon occurs frequently in Antarctica because of
ice crystals in the atmosphere that reflect and refract light. Halos are typically
rings of light circling the Sun or Moon, but they can also appear as pillars
and arcs of light.

Whiteout

Under whiteout conditions, it is difficult to judge distances,
perceive gradients or make out the horizon. Whiteouts can occur under different
weather conditions (for example blizzards or calm, overcast conditions) where
light is diffuse and it is hard to distinguish the surface from the sky.

Student activities

Gisdata (Note, at this site (a GIS programme) you can search by key words or place
names by clicking in the 'Query' box on the binoculars icon. A drop down
box will appear showing any locations that include the search term that are
within the map data base. Click on the desired location and it will appear
on the map. You might have to use the magnifying glass icons to zoom in to
see the selected location.)

Copy the data attached here into your own spreadsheet and do the following:

Choose a selection of stations from the spreadsheet that represent a range
of locations and elevations across Antarctica.

Draw climate graphs for the selected stations. (Months of the year along
the X-axis, weather variables along the Y-axis.) Plot mean monthly temperatures
as points connected by a line, and (where data are available) plot mean monthly
precipitation as bars for each month. (Hint: you need two Y-axis scales if
plotting both temperature and precipitation.)

For each station chosen, calculate the mean annual temperature, the total
annual precipitation (where data are available), and the mean annual wind velocity.
Also identify the maximum and minimum values for each variable, and calculate
the annual ranges.

2b. Write short paragraphs to describe the nature of the climate at each selected
station. (Abbreviated descriptions can also be added on to your Antarctica
base map next to the relevant research station.)

2c. Identify the station on the spreadsheet with the lowest mean annual temperature.
What factors cause this station to be the coldest in Antarctica?

2d. Identify the station on the spreadsheet with the highest average windspeed.
What factors cause strong winds here?

3. Write a short essay to explain the differences in climate seen between
the different stations. Discuss a variety of different weather variables and
consider factors such as latitude, altitude, and proximity to the Southern
Ocean in your essay.

For further data on Antarctica's weather and climate (including average min
and average max monthly temperatures) you can follow these links: